Joe Bullock: said he and people like him needed to be involved in the Labor party because 'the buggers might win'. Photograph: abc.net.au

Labor's lead Senate candidate in the rerun West Australian Senate ballot has been forced to write to all Labor members in the state on the eve of the election, apologising for suggesting many of them were "mad".

"I am writing to apologise for the offensive remarks I made last year which have been widely reported in the media today. My comments were ill-considered, and I apologise unreservedly," he said in the emailed apology.

"I have the utmost respect for Labor members and our supporters and share your concern for the interests of working people in this state and this country.”

He also apologised to his running mate, Louise Pratt, after questioning whether she really was a lesbian since her partner had had a sex change.

"I have enormous respect for Louise, she has served the party and this state magnificently for over a decade and I'm confident that with the support of us all she'll be returned to the Senate tomorrow. Both Louise and I need your support on booths tomorrow and I know we can count on you," he said.

In a speech to a Christian group, the Dawson Society last November, available on its website, Bullock said people like him and the Christian audience he was addressing needed to be involved in the Labor party because “the buggers might win, and if they win they either drive the country straight off the cliff or there are some people around to say hello, we really should reconsider this policy, this isn’t the right thing to do”.

“The problem the Labor party has got is this … when the Labor party – and sooner or later I am going to have to stop thinking of the Labor party as ‘them’ and start accepting some ownership of it – when the Labor party says to voters trust us, we have your interests at heart, the voters don’t trust them,” Bullock said.

“And the voters are right, the Labor party haven’t demonstrated they are capable of being trusted to look after the interests of working people and their families.”.

Bullock, who worked with Abbott more than 30 years ago to take over the Sydney University Liberal club and had already been elected to the Senate in last September’s election at the time of the speech, said of the prime minister: “I know his core beliefs, I know what they were, because we were close and politically active together … I think he has the potential to be a good prime minister.”

After the Australian newspaper reported parts of the speech on Friday, including Bullock’s claim that the unions provide the “commonsense ballast” to “direct” the Labor party, which is full of “mad” members, Bullock apologised for any offence.

Asked about former prime minister Rudd’s Christian faith, he said: “Who knows, he’d change his mind over a cup of coffee.”

And he said: “The time is coming where faith needs to be protected from politics … the anti-discrimination movement is forcing religious belief into the four walls of a church. I am conscience of the movement for homosexual marriage and what that could mean for Catholic schools, where homosexuality could be required to be advocated as a moral equivalent to heterosexual marriage, I am concerned Catholic hospitals could be forced to recommend abortions … this is politics invading freedom of religion … freedom of religions is the freedom to practice your religion and that means taking your beliefs out of your church and living them in your life.”

He said it was a “good question” to consider how he should vote on a foreign aid budget that was in part spent on birth control services that included abortion, and he would need to consider his view.

He said it was “remarkable” that those advocating same-sex marriage had “claimed the moral high ground” and advised the audience: “We need to fight back.”

The prime minister immediately seized on the speech, saying it proved there was “division and dysfunction” at the heart of the WA Senate team and proved Labor was “not up to the task of government”.

Bullock and Pratt appeared side by side at a campaign event on Friday targeting the state coalition’s record on school funding.

“I joined the Labor party in 1978 and I have supported the Labor party ever since … The central feature of the Labor party is its concern for working people and their families. The unions insist on maintaining that focus and I think that is a wonderful thing,” Bullock said when questioned about the controversial speech.

Pratt said she and Bullock “have a lot more in common than we would ever have that is different … we champion the rights of ordinary west Australians”.

It has emerged at the end of a dramatic campaign for the Senate vote in which – as Guardian Australia reported last week – Clive Palmer’s Palmer United party outspent the major parties by a factor of at least 10, and 75 elderly voters will be forced to vote again after their prepoll ballots were placed in an unsecured ballot box.

The result will be crucial to the make-up of the crossbench upon which the Abbott government will rely for passage of all legislation opposed by Labor and the Greens.

The opposition leader, Bill Shorten, has said Bullock is “exactly” the kind of person who should represent the Labor party and after the speech emerged it was reported said he stood by that endorsement.

The Labor frontbencher Anthony Albanese said Bullock “of course, is a colourful character”.

“One thing I know about Joe is that he has spent his life standing up for working people as a union official representing shop assistants," Albanese told ABC radio on Friday. "I know that if he is elected to the Senate tomorrow, as I expect him to be, he will stand up for working people in the national parliament."

Labor party sources were dismayed at the speech and conceded it was damaging to the party’s prospects.